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Garlock Fault: Re-assessing past stream offsets at Oak Creek Canyon and predicting future fault displacements

Kelley A. Shaw, & Graham M. Kent

Published August 15, 2017, SCEC Contribution #7845, 2017 SCEC Annual Meeting Poster #145

Numerous paleoseismic investigations have been undertaken along the western and central traces of the Garlock fault. Some of the older investigations relied on rough topographic data for cross fault reconstructions to estimate slip rates. Re-assessing these studies with publicly-available high-resolution LiDAR collected by Earthscope can potentially refine those measurements. LaViolette et al. (1980) looked at offset Pleistocene channels in Oak Creek Canyon and found a total offset of 300 m and corresponding Quaternary slip rate of 1.6 to 3.3 mm/yr. This rate is significantly lower than slip rates from other studies 30 km to the west, i.e., 7.6 mm/yr at Clark Wash (McGill et al., 2009). Reconstruction of the cross fault stream channels via LiDAR reveals different offset results for the Oak Creek Canyon site. Looking back at other past investigations, given more recent higher resolution data, could help refine displacement measurements along active faults in California, which could reduce the uncertainty of estimated seismic hazard and likelihoods of surface fault rupture. Ten kilometers to the east of Oak Creek Canyon, the planned alignment of the California High Speed Rail will cross the western segment of the Garlock fault. A probabilistic fault displacement analysis was performed for this crossing to estimate expected displacement over certain future time periods. Multiple rupture scenarios along the fault were considered based on evidence from past studies of ruptures extending across gateways. The approach used relates the frequency of slip events at the site to the geometry and frequency of earthquakes on the fault and the probability that an individual earthquake will be associated with surface rupture. Only primary fault displacement was considered. Expected displacement at a 10% probability of exceedance (PE) in 50 years varies from 40 cm to 75 cm depending on the rupture scenario. At a PE = 2% in 50 years, expected displacement is on the order of a few meters.

Shaw, K. A., & Kent, G. M. (2017, 08). Garlock Fault: Re-assessing past stream offsets at Oak Creek Canyon and predicting future fault displacements. Poster Presentation at 2017 SCEC Annual Meeting.

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Earthquake Geology